Discharge device including channel type electron multiplier having ion adsorptive layer

ABSTRACT

An image intensifier or other tube including a photocathode or the like and a channel-type electron multiplier therefor. The multiplier includes a perforated glass plate with a conductive electrode layer evaporated on each of two opposite sides thereof. Each of the electrodes has a plurality of holes therethrough that lie in registration with the plate holes. A layer of titanium is evaporated onto the output electrode. A substantial increase in photocathode life is then achieved. Alternatively, the said three layers need not be employed. Instead, the output electrode itself may be made of titanium. In this case, no other layer need be evaporated over the output electrode.

United States Eatent Cuny 1 Mar. 11, 1975 [541 DISCHARGE DEVICE-INCLUDING 3,497,759 2/1970 Manley 315/11 CHANNEL TYPE ELECTRON MULTIPLIER wil at U 6118011 6! a HAVING ION ADSORPTIVE LAYER 3,609,062 9/1971 Zucchinelli et al. 313/178 x John J. Cuny, Granada Hills, Calif.

Assignee: International Telephone and Telegraph Corporation, New York, NY.

Inventor:

Filed: Feb. 16, 1973 Appl. No.: 333,437

Related U.S.Application Data Continuation of Ser. No. 141,850, May 10, I971, abandoned U.S. Cl. 313/105, 313/106 Int. Cl. H0lj 43/28, l-lOlj 39/04 Field of Search 313/104, 95

References Cited UNITED STATES PATENTS Primary Examiner-Robert Segal Attorney, Agent, or Firm-John T. OHalloran; Menotti J. Lombardi, Jr.; Edward Goldberg [57] ABSTRACT An image intensifier or other tube including a photocathode or the like and a channel-type electron multiplier therefor. The multiplier includes a perforated glass plate with a conductive electrode layer evaporated on each of two opposite sides thereof. Each of the electrodes has a plurality of holes therethrough that lie in registration with the platevholes. A layer of titanium is evaporated onto the output electrode. A substantial increase in photocathode life is then achieved. Alternatively, the said three layers need not be employed. Instead, the output electrode itself may be made of titanium. In this case, no other layer need be evaporated over the output electrode 1 Claim, 5 Drawing Figures DISCHARGE DEVICE INCLUDING CHANNEL TYPE ELECTRON MULTIPLIER HAVING ION ADSORPTIVE LAYER This is a continuation of application Ser. No. 141,850 filed May 10, 1971, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to electron multipliers, and more particularly, to a channel-type electron multiplier and an image tube or the like incorporating the same.

In the past, in an image intensifier, it has been the practice to supply a channel-type electron multiplier with primary electrons from a photocathode, and to display the electron output of the multiplier on a phosphor screen. See US. Pat. No. 3,449,582. However, it has been extremely difficult to consistently construct such tubes in a manner such that the photocathodes have a long useful life. The photocathodes regularly have a useful life so short that they are completely unsuited to any production in quantity. The photocathodes often fail within a day or two to produce a suitable electron output as a function of constant, normal illumination.

SUMMARY OF THE INVENTION In accordance with the device of the present invention, the above-described and other disadvantages of the prior art are overcome by providing a positive ion adsorption layer at one side of the dielectric plate of a channel-type electron multiplier.

The positive ion adsorption layer works unexpectedly to increase the photocathode life a substantial extent.

In accordance with a special feature of the invention, the positive ion adsorption layer is located on the multiplier side which faces the phosphor screen.

It is not obvious why the positive ion adsorption layer substantially increases photocathode life. This is especially true where the positive ion adsorption layer is located on the screen side of the multiplier. Thatis, one would not expect any ion adsorption on the screen side to be of any value to the photocathode. It could be expected that the sheer size and mass of the multiplier would block any substantial flow of positive ions from the multiplier output side to the photocathode on the input side thereof. However, the location of the positive ion adsorption layer on the screen side of the multiplier, in fact, substantially reduces photocathode poisoning and substantially increases photocathode life.

One explanation for the phenomenon may be that there isa relatively large space between the multiplier and screen. The screen has a relatively large area, and is maintained at, for example, 5,000 volts positive with respect to the multiplier output electrode. There may thus be a greater chance that positive ions will be beaten out of the screen by the high speed electron bombardment of the screen. Typically, the multiplier output electrode is 1,000 volts positive with respect to the photocathode. The difference between the output electrode and screen potentials is thus substantially greater than the difference between the potentials of following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to be regarded as merely illustrative:

FIG. 1 of a longitudinal sectional view, partly in elevation, of an image intensifier constructed in accordance with the present invention;

FIG. 2 is a perspective view of an electron multiplier shown'in FIG. 1;

FIG. 3 is a broken away front elevational view of the multiplier shown in FIG. 2;

FIG. 4 is a longitudinal sectional view of a portion of the multiplier taken on the line 44 shown in FIG. 3; and

FIG. 5 is a longitudinal sectional view similar to that of FIG. 4 illustrating an alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an image intensifier is indicated at 10 including an evacuated, transparent glass envelope 11 having a cylindrical wall 12, and two circular plate end faces 13 and 14.

A photocathode 15 is coated onto the interior surface of end face 13. A phosphor screen 16 is coated onto interior surface of end face 14. An electron multiplier 17 is fixed inside envelope 11 between photocathode 15 and phosphor screen 16. As is evident, photocathode 15 and phosphor screen 16 are fixed relative to and inside of envelope 11, as is conventional.

All of the component parts of multiplier 17 are shown in elevation in FIG. 1 for clarity. Multiplier 17 includes an input electrode 18, a glass plate 19, an output electrode 20 and a layer 21 of titanium.

For purpose of definition herein and in the claims, the phrase electron multiplier is hereby defined to include plate 19 with or without electrodes 18 and 20, and with or without layer 21. Furthermore, the phrase electron multiplier includes plate 19 with either one or both or neither of electrodes 18 and 20.

Although it is not critical, photocathode l5 and phosphor screen 16 may be made in the shape of circular concentric discs. As shown in FIG. 2, multiplier 17 may have a circular or cylindrical construction concentric with photocathode 15 and phosphor screen 16. The stipped area on the face of layer 21 indicates holes therein. Similarly, plate 19 has holes and electrodes 18 and 20 have holes and layer 21 has holes. Each hole in electrode 18 has a corresponding hole in plate 19, electrode 20 and layer 21. Each of the holes corresponding to one hole in electrode 18 lie in registration therewith. Electrodes l8 and 20 are conductive layers which are evaporated onto the two opposite circular faces of plate 19. Further, layer 21 may be evaporated onto electrode 20 in the conventional manner by conventional apparatus.

Holes are indicated at 22 in FIG. 3 through electrode 18. FIG. 3 is a greatly enlarged elevational view of a portion of the circular face of electrode 18 not in contact with a face of plate 19.

As shown in FIG. 4, holes 23 in electrode 18 lie in registration with holes 24 in plate 19. Holes 25 in electrode 20 also lie in registration with plate holes 24.

Holes 26 in layer 21 lie in registration with electrode holes 25.

An alternative embodiment of the invention is shown in FIG. 5 including an electron multiplier 27 having a glass plate 28, an input electrode 29 and an output electrode 30. In this case, plate 28 and electrode 29 may be identical to plate 19 and electrode 18, respectively. Electrode 30 may be an evaporated layer of titanium. Layer 30 thus can serve two purposes at the same time. That is, it is not necessary to include both of the layers 20 and 21, as shown in FIG. 5. The layer 30 can serve the purpose of each of these layers at the same time. Layer 30 may be maintained at a potential to act as an output electrode. At the same time, it may be an evaporated layer of titanium and serve as an ion adsorption layer.

As shown in FIG. 1, a source of potential 31 may be employed to operate tube 10. Typically, photocathode may be maintained at ground potential. Electrode 18 may be maintained at apotential of 100 volts positive with respect to ground. Electrode 20 may be maintained at a potential of about 1,000 volts positive with respect to ground. Phosphor screen 16 may be maintained at a potential of about 5,000 volts positive with respect to ground.

In the operation of the image intensifier 10, photocathode 15 will emit primary electrons at a rate depending upon the intensity of illumination thereof.

The primary electrons are accelerated through electrode holes 23 and eventually are drawn to the higher potential surfaces of plate holes 24. The impact of primary electrons thereon causes the release of secondary electrons. The ratio of secondary electrons to primary electrons is greater than unity. The first secondary electrons generated multiply still furhter by being drawn down plate holes 24 and impacting the cylindrical walls of holes 24 again. The number of times that the process is repeated depends upon the length of the plate holes 24. Ultimately, a multiplied electron flow will exit out of holes 24, 25 and 26, in succession. The electron output of multiplier 17 is then accelerated toward and bombards phosphor screen 16. The light output of phosphor screen 16 is then greater than the light input through envelope faceplate 13.

Titanium layers 21 and 30 apparently adsorb a large number of the positive ions pulled out of phosphor screen 16 from bombardment thereof by the electron output of multiplier 17. At any rate, the useful life of photocathode 15 is substantially increased.

What is claimed is:

1. An electron tube multiplier device comprising: an evacuated envelope, electrode means positioned within one end of said envelope for emitting primary electrons, adielectric plate positioned in the path of said primary electrons and having a plurality of holes extending completely therethrough from a first input side thereof to a second output side opposite said first side, said plate holes having secondary electron emissive resistive surfaces emitting secondary electrons in response to impingement of said primary electrons, electrode means positioned at the other end of said envelope spaced from and facing said second output side for receiving said secondary electrons and emitting positive ions in response thereto; a first electrode layer on said first side having a plurality of holes in registration with said holes in said plate, a conductive layer on said second side having a plurality of holes in registration with said holes in said plate, a positive ion adsorption second electrode layer including titanium metal on said conductive layer on said second side, said ion adsorption layer having a plurality of holes extending completely therethrough in registration with said plate holes, and said conductive layer holes said ion adsorption layer receiving and adsorbing said positive ions from said electrode means at said other end, and means for applying potentials between successive electrodes including said electrode means emitting primary electrons and said first and second electrode layers and said 

1. An electron tube multiplier device comprising: an evacuated envelope, electrode means positioned within one end of said envelope for emitting primary electrons, a dielectric plate positioned in the path of said primary electrons and having a plurality of holes extending completely therethrough from a first input side thereof to a second output side opposite said first side, said plate holes having secondary electron emissive resistive surfaces emitting secondary electrons in response to impingement of said primary electrons, electrode means positioned at the other end of said envelope spaced from and facing said second output side for receiving said secondary electrons and emitting positive ions in response thereto; a first electrode layer on said first side having a plurality of holes in registration with said holes in said plate, a conductive layer on said second side having a plurality of holes in registration with said holes in said plate, a positive ion adsorption second electrode layer including titanium metal on said conductive layer on said second side, said ion adsorption layer having a plurality of holes extending completely therethrough in registration with said plate holes, and said conductive layer holes said ion adsorption layer receiving and adsorbing said positive ions from said electrode means at said other end, and means for applying potentials between successive electrodes including said electrode means emitting primary electrons and said first and second electrode layers and said electrode at said other end. 